1. Field of the Invention
The present invention relates to an illumination apparatus and a projection display apparatus, both of which utilize four kinds or more of color component lights.
2. Description of the Related Art
Conventionally, there has been known a projection display apparatus having: three imagers corresponding to three kinds of color component lights; a cross dichroic cube which combines the color component lights emitted from the three imagers; and a projection lens unit which projects the color component light combined by the cross dichroic cube.
Here, the cross dichroic cube has three light incident surfaces onto which the color component lights enter and one light emitting surface from which the color component lights are emitted. Therefore, when there are three kinds of color component lights entering the cross dichroic cube, the projection display apparatus needs to only have one cross dichroic cube as a color combiner.
Meanwhile, there has been proposed a projection display apparatus which utilizes four kinds or more of lights for the purpose of improving color reproducibility and luminance. For example, the projection display apparatus achieves improvement in the color reproducibility and the luminance by utilizing orange, yellow or cyan in addition to three colors of red, green and blue (see, for example, claims 1 and 4, as well as, FIG. 1 and the like in Japanese Patent Application Publication No. 2002-287247).
Here, in the case where the projection display apparatus utilizes four kinds or more of color component lights, the four kinds or more of color component lights cannot be combined by one color combiner (cross dichroic cube). Therefore, the projection display apparatus is required to have a plurality of color combiners (dichroic cubes or cross dichroic cubes).
For example, when it is required to combine four kinds of color component lights, the projection display apparatus obtains a combined light including the four kinds of color component lights, by obtaining two combined lights each including two kinds of color component lights, and by further combining the two combined lights. Note that the projection display apparatus may alternatively obtain a combined light including the four kinds of color component lights, by obtaining a combined light including three kinds of color component lights and, by further combining the combined light with one color component light. Moreover, the projection display apparatus may also obtain a combined light including the four kinds of color component lights, by obtaining a combined light including two kinds of color component lights, and by further combining the combined light with two kinds of color component lights.
Here, optical path length from each of imagers corresponding to the four kinds or more of color component lights to the projection lens unit is required to be the same. Moreover, it is required to provide a plurality of color combiners (dichroic cubes or cross dichroic cubes) between the imagers and the projection lens unit. Therefore, a back-focus of the projection lens unit is increased.
As a result, it is impossible to divert the projection lens unit used in the projection display apparatus which utilizes three kinds of color component lights. Thus, cost of the projection display apparatus is increased as a whole.